High-tension cable adapted for small currents



Jan. 17, 1928.

1,656,329 E. G. SIEVERT ET AL HIGH TENSION CABLE ADAPTED FOR SMALL CURRENTS Filed Nov. 11. 1925 In ven fors Ernst GusfafSz'everZ. and Hemfihy" vensson Patented Jan. 17, 1928.

PATENT OFFICE.

ERNST eusmv srnvnn'r AND anytime svnivsson,

OF SUNDBYBERG, NEAR STOCK- HOLM, SWEDEN.

HIGH-TENSION CABLE ADAP TED FOR SMALL CURRENTS.

Application filed November 11, 1925, Serial No. 68,442, and in Sweden December 6, 1924.

The present invention refers to an improvement in cables adapted for small cur-' rents, for instance to be used in Rontgen-ray apparatus. In such cables the cross-section of the conductor needs not, generally, amount to more than 1 or 2 mmfi'with're- 'gard to thecurrents transmitted. D

As to high tension currents, sucha reduced dimension of the conductor will, however, result in rather strong stresses on that part of the insulating material which is placed next to the conductor. On account of this the thiclmess of said layer must be cable will be the m nimum cross-section of the cable required fora certain breaking-down voltage is obtained when, at a proportion of the outer diameter of the cable insulation to the. conductor diameter equal to 2,72, the stress in the innermost surface of the insulating layer is equal to the permissible value. The minimum diameter of the cable in the present case should, thus, be obtained if the diameter of the conductor (useful cross-section) is increased and the thickness of the insulating material is decreased till said proportion of the outer diameter of the insulation to that of the conductor and further said stress on the innermost surfaceof the insulating layer are arrived at.

an increasing of the relatively expensive conductor will, however, result in considerably higher costs of the cable,and at the same time the cable will be practically inflexible.

' According to the present invention the resultaimed at will, however,v be obtained without increasing the diameter of the metallic conductor by making the layer placed next to the conductor conducting, for instance by introducing graphite, smokeblack or any electrically conducting material therein which allows a thorough mixing up with the insulating material; Byadapting the thickness of said conducting layer in such a way as to give the cable, according to the above,

in Fig. 2, the thickness of Such its most favorable dimensions, the same result is arrived at as if the metallic conductor had been increased in a corresponding degree, however quite unnecessary with regard to the small currents to .be transmitted.

For this as rubber, used.

In order that the nature of our invention maybe clearly understood, reference is to be had to the-accompanying drawings, in which Fig. l is'a cross-section of a known form of cable;

Fig. 2 is a cross-section of another" known form of cable; and

Fig. 3 is a cross-section of a cable constructed in accordance with our invention. In Fig. 1 a conductor 1 is Shown having a cross-section. corresponding to the current in question. The thickness of the necessary insulating layer 2 is supposed to have the value set forth by the figure. Whenincreasing the diameter of the conductor as shown the insulating 2 is supposed most favorable purpose insulating material. such gutta-percha, bakelite etc. may be layer may be decreased. Fig. to show a cable having the dimensions.

Finally, Fig. 3 shows a cable to the invention, and, in this case, the crosssectionof the metallic conductor is the same one as that shown in Fig. 1. Owing to the conductin g layer?) consisting of rubber mixed with smoke-black the most favorable crosssection of the cable will be larger than that shown in Fig. 2, and consequently, a considerable saving in material will be obtained whether the present invention is compared with the cable constructionshown in Fig. 1 or that in Fig. 2.

aving now particularly described the nature of our invention and the manner of its operation, what we claim is:

' A high tension insulated cable for smallaccording currents comprising a metallic conductor conductor, and being mixed with a conductthat the stress on the inner surface of the ing material so as to act as a conductor for insulating layer will only amount to the rial surrounding said current-conducting In testimony whereof We herewith afiix 5 rubber layer, the proportion of the diameter our signatures.

of the complete cable to the diameter of the ERNST GUSTAV SIEVERT.

conducting material being equal to 2.72, so HENNING SVENSSON.- I

the current, and a layer of insulating matepermissible Value thereof. 1 

